Heater current control device for A / F sensor

Abstract

To shorten a time until the temperature of a plurality of A / F sensors reach an activation temperature, while reducing a load on a power source system in a case where the A / F sensors are in a low-temperature state.SOLUTION: In a heater energization controller 11, when at least one of temperatures of A / F sensors 1(1), 1(2) detected by temperature detection units 18(1), 18(2) is below a predetermined value, a microcomputer 12 energizes heaters 4(1), 4(2) one by one to perform initial energization control for controlling energization switches 14(1), 14(2) so as to activate the A / F sensors 1(1), 1(2) in parallel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a device for detecting the state of gas contained in exhaust gas from an internal combustion engine, and relates to a device for energizing heaters of a plurality of A / F sensors each equipped with an activation heater. [Background technology]

[0002] Conventionally, a device for controlling the energization of heaters in a plurality of air-by-fuel (A / F) sensors with built-in heaters arranged in the exhaust path of an internal combustion engine is disclosed, for example, in Patent Document 1. When the A / F sensor and its heater are in a low temperature state immediately after starting the vehicle, a large current is required to energize the heater in order to increase the temperature of the A / F sensor and activate it.

[0003] Therefore, in Patent Document 1, electricity is first supplied to the heater of the A / F sensor located upstream of the exhaust path, and then electricity is supplied to the heater of the A / F sensor located downstream of the same, thereby limiting the current supplied to the heater and reducing the load on the battery and heater power supply system when the A / F sensor and its heater are in a low temperature state. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-232746 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned conventional technology, the A / F sensor in which the start of energization to the heater is delayed takes longer to reach the activation temperature, and the start of air-fuel ratio detection is delayed, resulting in a problem that the start of air-fuel ratio control of the internal combustion engine is delayed, and the amount of harmful substances emitted in the vehicle exhaust gas increases.

[0006] In addition, since only exhaust gas from the internal combustion engine contributes to the heating of the heater during the delayed energization, it depends on the condition of the internal combustion engine, and the heating efficiency varies compared to heating the A / F sensor with a built-in heater.For example, when starting the engine in cold regions, the A / F sensor and its heater are low in temperature, and it takes time for the internal combustion engine to warm up and the exhaust gas temperature to rise, so it may take a long time for the sensor to reach its activation temperature.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide an A / F sensor heater current control device that can reduce the load on the power supply system when the A / F sensor is in a low temperature state while shortening the time it takes for multiple A / F sensors to reach their activation temperature. [Means for solving the problem]

[0008] According to the heater energization control device of the A / F sensor of claim 1, when at least one of the temperatures of the plurality of A / F sensors equipped with activation heaters detected by the plurality of temperature detection units is equal to or lower than a predetermined value, the energization control unit: By PWM signal By energizing the heaters one by one, initial energization control is performed to control a plurality of energization switches so as to activate two or more A / F sensors in parallel.

[0009] With this configuration, when activating two or more A / F sensors in parallel during initial power control, power is applied to each of the multiple heaters one at a time, thereby reducing the load on the power supply system when the A / F sensor is in a low temperature state and shortening the time it takes for the multiple A / F sensors to reach their activation temperature.

[0010] Also, Claim 1According to the described A / F sensor heater energization control device, when the temperature of the A / F sensor targeted for activation exceeds a predetermined value, the energization control unit performs normal energization control in which energization is superimposed on two or more of the heaters. That is, when the energization control unit confirms that the temperature of the targeted A / F sensor exceeds a predetermined value, it transitions from initial energization control to normal energization control. Therefore, it is possible to transition to normal energization control when the load on the power supply system is reduced.

[0011] Also, Claim 1 According to the heater current control device for the A / F sensor described above, the current control unit also transitions to normal current control when the current flowing through the heater falls below a predetermined value, making it possible to transition to normal current control at the point when the load on the power supply system is more reliably reduced. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a functional block diagram showing a configuration of a heater current control device according to a first embodiment. [Diagram 2] Flowchart showing the control contents [Diagram 3] A diagram showing the PWM signals that drive the two energization switches and the energization current to the heater when transitioning from initial energization control to normal energization control. [Figure 4] FIG. 3 in the prior art [Diagram 5] A flowchart showing a process for calculating the duty ratio of a PWM signal in normal energization control. [Figure 6] FIG. 11 is a diagram showing the PWM signals for driving the two energization switches and the energization current to the heater when transitioning from the initial energization control to the normal energization control according to the second embodiment. [Figure 7] FIG. 13 is a functional block diagram showing the configuration of a heater current control device according to a third embodiment. [Figure 8] Flowchart showing the control contents DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (First embodiment) As shown in Fig. 1, A / F sensors 1(1) and 1(2) of this embodiment detect exhaust gas discharged from an internal combustion engine for a vehicle (not shown) and identify the state of gas contained in the exhaust gas, for example, the air-fuel ratio in the exhaust. The A / F sensor 1 is disposed in the exhaust passage of the internal combustion engine. The peripheral configurations of the A / F sensors 1(1) and 1(2) are symmetrical, so in the following description, unless there is a particular need to distinguish between the two, the reference numerals (1) and (2) will not be added.

[0014] The A / F sensor 1 includes a sensor element 3 and a heater 4 for heating and activating the sensor element 3. Power is supplied to the heater 4 from a heater power supply system 5. The heater power supply system 5 supplies power from a power source 6 to the heater 4 via a wire harness 7 and a fuse 8. The power supply is controlled by a heater current control device 11.

[0015] The heater energization control device 11 includes a microcomputer 12 and a heater drive control IC 13. The low potential terminal of the heater 4 is connected to ground inside the heater energization control device 11 via a energization switch 14, such as an N-channel MOSFET, and a resistor element 15.

[0016] Both ends of the resistive element 15 are connected to the input terminals of an amplifier 16 built into the heater drive control IC 13, and the output signal of the amplifier 16 is input to the microcontroller 12 via a communication line 17 connecting the control IC 13 and the microcontroller 12.

[0017] Both ends of the sensor element 3 included in the A / F sensor 1 are connected to input terminals of a temperature detection unit 18 included in the heater drive control IC 13. The temperature detection unit 18 detects the temperature of the sensor element 3 based on a change in impedance of the sensor element 3 obtained by applying a voltage to the sensor element 3. An output signal of the temperature detection unit 18 is input to the microcomputer 12 via a communication line 17. The microcomputer 12, which corresponds to a power supply control unit, outputs a drive signal to the gate of the power supply switch 14 as a PWM (Pulse Width Modulation) signal via the heater drive control IC 13.

[0018] Next, the operation of this embodiment will be described. As shown in Fig. 2, when the microcomputer 12 detects the temperatures of the A / F sensors 1(1) and 1(2) via the heater drive control IC 13 (S1), it judges whether the temperature of either of the A / F sensors 1 is equal to or lower than a predetermined value (S2). Here, the degree to which the "predetermined value" is set depends on the power supply capacity of the heater power supply system 5 and the characteristics of the heater 4, but is set to, for example, about 25°C, which is considered to be room temperature.

[0019] If the temperature is equal to or lower than a predetermined value (S2; YES), alternating energization control is performed as initial energization control (S4). As shown on the left side of Fig. 3, alternating energization control is a control in which the PWM signals output to the gates of energization switches 14(1) and 14(2) are signals with a duty ratio of 50% and opposite phases to each other, thereby energizing heaters 4(1) and 4(2) alternately.

[0020] During the alternating energization control, the microcomputer 12 detects the current flowing through the heaters 4(1) and 4(2) via the heater drive control IC 13 (S5). Then, it is determined whether the sum of the two current values ​​is equal to or less than a predetermined value (S6). If the sum of the current values ​​exceeds the predetermined value (NO), the process returns to step S4, and if it is equal to or less than the predetermined value (YES), the process moves to normal energization control (S3). As shown on the right side of FIG. 3, normal energization control is a control in which the duty ratios of the PWM signals output to the gates of the energization switches 14(1) and 14(2) are set arbitrarily to less than 100% to energize the heaters 4(1) and 4(2).

[0021] That is, in the alternate current control, only one of the heaters 4(1) and 4(2) is energized, and there is no period during which both are energized at the same time. In this way, by alternately energizing the heaters 4(1) and 4(2), the A / F sensors 1(1) and 1(2) are heated alternately, and these are activated in parallel. On the other hand, in the normal current control, there is a period during which both are energized at the same time. Note that if the temperatures of both A / F sensors 1 exceed the predetermined value (S2; NO), the process also proceeds to step S2.

[0022] In the conventional technology shown in Fig. 4, at the start of the energization control for activating the A / F sensors 1(1) and 1(2), current is supplied to both heaters 4(1) and 4(2) in a superimposed manner, so that the peak value of the sum of the energization currents is high. In contrast, at the start of the initial energization control of the present embodiment shown in Fig. 3, current is supplied alternately to heaters 4(1) and 4(2), so that the peak value of the sum of the currents is lower.

[0023] In normal energization control, as shown in FIG. 5, when the microcomputer 12 starts calculating the duty ratio (S11), it detects the temperature of the A / F sensor 1(1) and the energization current of the heater 4(1) (S12), and calculates the duty ratio of the PWM signal to be output to the gate of the energization switch 14(1) based on the temperature and current (S13).

[0024] Similarly, the microcomputer 12 then detects the temperature of the A / F sensor 1(2) and the current flowing through the heater 4(2) (S14), and calculates the duty ratio of the PWM signal to be output to the gate of the current-carrying switch 14(2) based on the temperature (S15). When the calculation of the duty ratio is completed (S16), the microcomputer 12 waits until the next calculation cycle is reached, that is, until the carrier cycle of the PWM control has elapsed (S17). If the current flow control to the heater 4 is still continuing at that point (S18; YES), the process returns to step S11.

[0025] As described above, in this embodiment, in heater energization control device 11, if at least one of the temperatures of A / F sensors 1(1), 1(2) detected by temperature detection units 18(1), 18(2) is below a predetermined value, microcomputer 12 performs initial energization control, which controls energization switches 14(1), 14(2) to activate A / F sensors 1(1), 1(2) in parallel by energizing heaters 4(1), 4(2) one by one.

[0026] With this configuration, when activating A / F sensors 1(1), 1(2) in parallel during initial power control, power is applied to heaters 4(1), 4(2) one at a time, thereby reducing the load on power supply system 5 when A / F sensor 1 is in a low temperature state and shortening the time it takes for the two A / F sensors 1 to reach their activation temperature.

[0027] Furthermore, when the temperature of the A / F sensor 1 that has been activated exceeds a predetermined value or the current passed through the heater 4 falls to or below a predetermined value, the microcomputer 12 performs normal current control to pass current to the heaters 4(1), 4(2) in a superimposed manner. That is, when the microcomputer 12 confirms via the current detection unit 16 that the current flowing through the power supply system 5 to the heater 4 falls to or below a predetermined value, the microcomputer 12 shifts from the initial current control to the normal current control. Therefore, when the load on the power supply system 5 is reduced, the control can shift to the normal current control.

[0028] Furthermore, the microcomputer 12 controls the energizing switch 14 with a PWM signal, and when performing initial energization control, outputs PWM signals with opposite phases, with a maximum duty ratio of 50%. In normal energization control, the duty ratio of the PWM signal is calculated individually for each constant control period based on the temperature or the current, and set to an arbitrary value. As a result, in initial energization control, alternating energization control can be performed by easily setting the duty ratio, and in normal energization control, the duty ratio of the PWM signal can be appropriately set based on the temperature or the current.

[0029] Second embodiment Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted, and only the different parts will be described. In the second embodiment shown in FIG. 6, the setting of each duty ratio in the initial energization control is different from that in the first embodiment. In the first embodiment, the duty ratios of the two PWM signals are equally set to 50%, but in the second embodiment, one duty ratio is set to be greater than 50% and the other duty ratio is set to be less than 50%. The sum of the two duty ratios is set to 100%. By controlling in this way, it is possible to preferentially activate the A / F sensor that needs to be activated earlier.

[0030] Third embodiment 7 includes a microcomputer 22 and an A / F sensor detection IC 23 that replaces the heater drive control IC 13. The A / F sensor detection IC 23 includes only a temperature detection unit 18, and an output port of the microcomputer 22 is directly connected to the gate of the energization switch 14. In other words, the microcomputer 22 directly drives the gate of the energization switch 14 without going through a drive IC.

[0031] The drains of the energizing switches 14(1) and 14(2) are both connected to the upper end of a common resistive element 15. That is, the microcomputer 23 detects the current flowing through the heaters 4(1) and 4(2) by using one resistive element 15 and amplifier 16.

[0032] Next, the operation of the third embodiment will be described. As shown in Fig. 8, in the third embodiment, steps S7 and S8 are executed instead of steps S5 and S6 in the first embodiment. That is, when step S4 is executed, the temperature of the heater 4 is detected by the temperature detection unit 18 (S7). Then, it is determined whether or not both of the temperatures of the two heaters 4 exceed a predetermined value (S8), and if both exceed the predetermined value (YES), the process proceeds to step S3.

[0033] In the above process, the current flowing through the heater 4 detected by the resistance element 15 and the amplifier 16 is not used. However, the detected current is used, for example, in a process for monitoring the deterioration state of the A / F sensor 1. As described above, the heater energization control device 21 of the third embodiment can be configured on a smaller scale than the heater energization control device 11 of the first embodiment.

[0034] (Other embodiments) The number of A / F sensors may be three or more. The configuration of the third embodiment may be applied to the control of the first embodiment. The energizing switch is not limited to a MOSFET, but may be a power transistor, an IGBT, or the like. Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0035] In the drawing, 1 is an A / F sensor, 3 is a sensor, 4 is a heater, 5 is a heater power supply system, 11 is a heater power control device, 12 is a microcomputer, 13 is a heater drive control IC, 14 is a power switch, 15 is a resistive element, 16 is an amplifier, and 18 is a temperature detection unit.

Claims

1. The device detects the state of gas contained in exhaust gas from an internal combustion engine, and energizes a plurality of A / F (Air By Fuel) sensors (1(1), 1(2)) each having an activation heater (4(1), 4(2)), A plurality of temperature detection units (18(1), 18(2)) for detecting temperatures of the plurality of A / F sensors; a plurality of energizing switches (14(1), 14(2)) respectively disposed in paths for energizing the plurality of heaters; an energization control unit (12, 22) that controls the on / off of each of the plurality of energization switches; a current detection unit (15, 16) for detecting a current passed through the heater, The energization control unit controls the energization switches by a PWM (Pulse Width Modulation) signal, when at least one of the plurality of temperatures detected by the plurality of temperature detection units is equal to or lower than a predetermined value, an initial energization control is performed in which the plurality of energization switches are controlled so as to activate two or more A / F sensors in parallel by energizing the plurality of heaters one by one using the PWM signal; When the temperature of the A / F sensor to be activated exceeds the predetermined value, the control is switched to a normal energization control in which two or more of the plurality of heaters are energized in a superimposed manner; The heater current control device for an A / F sensor also transitions to the normal current control when the current falls below a predetermined value.

2. 2. The heater current control device for an A / F sensor according to claim 1, wherein the current control unit calculates a duty ratio of the PWM signal based on at least one of the temperature and the current during the normal current control.

3. 3. The heater current control device for an A / F sensor according to claim 2, wherein the current control unit calculates the duty ratio individually for each constant control period.

4. 4. The heater current control device for an A / F sensor according to claim 2, wherein the current control unit sets the duty ratios of the plurality of PWM signals to arbitrary values ​​when performing the normal current control.

5. The number of the A / F sensors is "2", 4. The heater current control device for an A / F sensor according to claim 2, wherein the current control unit outputs PWM signals having mutually opposite phases with the maximum value of the duty ratio set to 50% when performing the initial current control.

6. The number of the A / F sensors is "2", 4. The heater current control device for an A / F sensor according to claim 2 or 3, wherein the current control unit, when performing the initial current control, sets the sum of the duty ratios of the two PWM signals to be 100% or less, and inverts one PWM signal to generate the other PWM signal.

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